DESCRIPTION: The primary function of the Transgenic Mouse Core is to generate transgenic mice by microinjection of recombinant DNA into mouse embryo. Transgenic mice are increasingly being used for studies of neuronal development and neuron-specific gene expression. Experiments using transgenic mice include: a) studies of cis-acting regulatory sequences that direct gene expression to specific neuronal cell types; b) studies of inappropriate synthesis of cell surface markers that are essential for normal neuronal morphogenesis; c) studies of neuronal maturation, cell cycle control and apoptosis; and d) studies of axonal path-finding. Such studies contribute to disorders that can lead to mental retardation. The recombinant DNA constructs to be used for making transgenic mice will be generated by the user laboratories, but the core until will purify the DNA fragments for microinjection. After injection, the embryos will be reimplanted into pseudopregnant foster mothers for development to term. After the mice are born and of weaning age, the Core will ear tagged the mice for identification, after which the animals will be transferred to individual investigators for further characterization. Another function to be served by the core is the cryopreservation of transgenic mouse lines. For these experiments, the individual investigators will provide superovulated pregnant females to the Core, and mouse embryos at the one cell stage will be harvested and cryopreserved in artificial insemination straws using standard methods. The success of cryopreservation will be monitored by recovering embryos from one straw and examining the efficiency with which the embryos develop to the blastocyst stage in vitro.